Originally Posted by sniddy

Also I have quite a few 5* girls nearing max so this will be a boon to me

EDIT - ALSO the keys given out by the challenge dungeons?

They're the same keys you get from the event stages, called "Manyu Keys". They're for summoning this amazing stage that gives a bunch of Manyus (the type depends on which type you choose to summon).

EDIT: Oh right, forgot to mention why they don't do anything. Basically, the devs didn't implement them yet. Technically we're not supposed to have them by Event 70, however our Event 70 is DMM's Event 74, which did have them.